Wet electrolytic capacitor

ABSTRACT

A wet electrolytic capacitor that contains a casing that contains a sidewall extending to an upper end to define an opening is provided. The sidewall further defines an inner surface that surrounds an interior. At least one anode and at least one cathode are positioned within the interior of the casing, wherein the cathode contains an electrochemically-active material and further wherein an anode lead extends from the anode. A working electrolyte is in electrical contact with the anode and the electrochemically-active material. The capacitor also comprises a lid assembly that contains a lid positioned on an upper end of the casing sidewall, wherein the lid defines an orifice through which a tube extends. The tube accommodates the anode lead that extends from the anode. A dielectric layer is formed on a surface of the tube.

BACKGROUND OF THE INVENTION

An implantable cardioverter-defibrillator (“ICD”) is a medical devicecombining a cardioverter and a defibrillator into a single implantableunit. One type of ICD is implanted intravascularly or intracardially,having leads positioned within the heart as well as being attached tothe outer surface of the heart. Such ICDs require the plurality of highenergy capacitors to provide about 35 to 40 joules of energy perelectrical impulse, as well as having a high voltage per electricalimpulse in the range of 700 to 800 volts to properly defibrillate, forexample, a patient suffering from ventricular fibrillation. Another kindof ICD is implanted subcutaneously and includes leads that are placedunder the skin and without direct contact with the heart. Such ICDs arealso known in the art as “subcutaneous ICDs.” The electrical impulse ina subcutaneous ICD needs to pass through muscles, the lungs and bones todefibrillate the heart as the leads are placed subcutaneously and arenot in contact with the heart. As such, subcutaneous ICDs must employeven higher energy and voltage levels than intracardiac ICDs. Wetelectrolytic capacitors are used in most state of the art ICDs due totheir ability to store high energy levels as well as their ability tomaintain high voltages, and thus have a high volumetric efficiency. Themost common capacitor shape used in ICDs is in the form of a half circleor “D shape.” Such D-shaped capacitors are not, however, suitable foruse in many types of implantable subcutaneous devices due to their lowratio between capacitance and size. While cylindrically-shapedcapacitors seem to be an ideal candidate, such capacitors oftenexperience increased DC leakage current.

As such, a need still exists for an improved wet electrolytic capacitorfor use in subcutaneous ICDs.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a wetelectrolytic capacitor is disclosed that comprises a casing thatcontains a sidewall extending to an upper end to define an opening,wherein the sidewall further defines an inner surface that surrounds aninterior. At least one anode and at least one cathode are positionedwithin the interior of the casing, wherein the cathode contains anelectrochemically-active material and further wherein an anode leadextends from the anode. A working electrolyte is in electrical contactwith the anode and the electrochemically-active material. The capacitoralso comprises a lid assembly that contains a lid positioned on an upperend of the casing sidewall, wherein the lid defines an orifice throughwhich a tube extends. The tube accommodates the anode lead that extendsfrom the anode. A dielectric layer is formed on a surface of the tube.

Other features and aspects of the present invention are described inmore detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a cross-sectional view of one embodiment of a lid assemblythat may be used to seal the wet electrolytic capacitor of the presentinvention;

FIG. 2 is a cross-sectional view of one embodiment of the wetelectrolytic capacitor of the present invention;

FIG. 3 is a side view of the wet electrolytic capacitor of FIG. 1; and

FIG. 4 is a top view of the wet electrolytic capacitor of FIG. 1, shownwithout a lid and sealing assembly.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention.

Generally speaking, the present invention is directed to a wetelectrolytic capacitor that contains a casing having a sidewallextending to an opening. The sidewall defines an inner surface thatsurrounds an interior of the casing. An anode, cathode, and workingelectrolyte are positioned within the interior of the casing.Furthermore, a lid assembly seals the opening of the casing. The lidassembly contains a lid (e.g., tantalum) that defines an internalorifice. A tube extends through the orifice that is of a size and shapesufficient to accommodate an anode lead that extends from the anode. Thetube is generally formed from a valve metal, such as tantalum, niobium,aluminum, nickel, hafnium, titanium, silver, alloys thereof (e.g.,electrically conductive oxides), and so forth. Notably, a dielectriclayer is formed on a surface (inner and/or exterior surfaces) of thetube. Without intending to be limited by theory, it is believed that thedielectric layer can help to prevent the tube from direct contact withthe working electrolyte and thus minimize DC leakage current. To helpfurther minimize leakage current, the thickness of the dielectric layeron the tube typically ranges from about 10 nanometers to about 1,000nanometers, in some embodiments from about 15 nanometers to about 800nanometers, in some embodiments from about 20 nanometers to about 600nanometers, and some embodiments, from about 30 nanometers to about 500nanometers.

Various embodiments of the present invention will now be described infurther detail.

I. Anode

The anode(s) of the electrolytic capacitor typically include a porousbody that may be formed from a valve metal composition. The valve metalcomposition contains a valve metal (i.e., metal that is capable ofoxidation) or valve metal-based compound, such as tantalum, niobium,aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitridesthereof, and so forth. For example, the valve metal composition maycontain an electrically conductive oxide of niobium, such as niobiumoxide having an atomic ratio of niobium to oxygen of 1:1.0±1.0, in someembodiments 1:1.0±0.3, in some embodiments 1:1.0±0.1, and in someembodiments, 1:1.0±0.05. For example, the niobium oxide may beNbO_(0.7), NbO_(1.0), NbO_(1.1), and NbO₂. Examples of such valve metaloxides are described in U.S. Pat. No. 6,322,912 to Fife; U.S. Pat. No.6,391,275 to Fife et al.; U.S. Pat. No. 6,416,730 to Fife et al.; U.S.Pat. No. 6,527,937 to Fife; U.S. Pat. No. 6,576,099 to Kimmel, et al.;U.S. Pat. No. 6,592,740 to Fife, et al.; and U.S. Pat. No. 6,639,787 toKimmel, et al.; and U.S. Pat. No. 7,220,397 to Kimmel, et al., as wellas U.S. Patent Application Publication Nos. 2005/0019581 to Schnitter;2005/0103638 to Schnitter, et al.; 2005/0013765 to Thomas, et al.

To form an anode, a powder of the valve metal composition is generallyemployed. The powder may contain particles any of a variety of shapes,such as nodular, angular, flake, etc., as well as mixtures thereof.Particularly suitable powders are tantalum powders available from CabotCorp. (e.g., C255 flake powder, TU4D flake/nodular powder, etc.) and H.C. Starck (e.g., NH175 nodular powder). The powder may be formed usingtechniques known to those skilled in the art. A precursor tantalumpowder, for instance, may be formed by reducing a tantalum salt (e.g.,potassium fluotantalate (K₂TaF₇), sodium fluotantalate (Na₂TaF₇),tantalum pentachloride (TaCl₅), etc.) with a reducing agent (e.g.,hydrogen, sodium, potassium, magnesium, calcium, etc.). Any of a varietyof milling techniques may be utilized in the present invention toachieve the desired particle characteristics. For example, the powdermay be dispersed in a fluid medium (e.g., ethanol, methanol, fluorinatedfluid, etc.) to form a slurry. The slurry may then be combined with agrinding media (e.g., metal balls, such as tantalum) in a mill. Thenumber of grinding media may generally vary depending on the size of themill, such as from about 100 to about 2000, and in some embodiments fromabout 600 to about 1000. The starting powder, the fluid medium, andgrinding media may be combined in any proportion. For example, the ratioof the starting valve metal powder to the grinding media may be fromabout 1:5 to about 1:50. Likewise, the ratio of the volume of the fluidmedium to the combined volume of the starting valve metal powder may befrom about 0.5:1 to about 3:1, in some embodiments from about 0.5:1 toabout 2:1, and in some embodiments, from about 0.5:1 to about 1:1. Someexamples of mills that may be used in the present invention aredescribed in U.S. Pat. Nos. 5,522,558; 5,232,169; 6,126,097; and6,145,765.

Milling may occur for any predetermined amount of time needed to achievethe target specific surface area. For example, the milling time mayrange from about 30 minutes to about 40 hours, in some embodiments, fromabout 1 hour to about 20 hours, and in some embodiments, from about 5hours to about 15 hours. Milling may be conducted at any desiredtemperature, including at room temperature or an elevated temperature.After milling, the fluid medium may be separated or removed from thepowder, such as by air-drying, heating, filtering, evaporating, etc. Forinstance, the powder may optionally be subjected to one or more acidleaching steps to remove metallic impurities. Such acid leaching stepsare well known in the art and may employ any of a variety of acids, suchas mineral acids (e.g., hydrochloric acid, hydrobromic acid,hydrofluoric acid, phosphoric acid, sulfuric acid, nitric acid, etc.),organic acids (e.g., citric acid, tartaric acid, formic acid, oxalicacid, benzoic acid, malonic acid, succinic acid, adipic acid, phthalicacid, etc.); and so forth.

Although not required, the powder may be agglomerated using anytechnique known in the art. Such powders may be agglomerated in avariety of ways, such as through one or multiple heat treatment steps ata temperature of from about 700° C. to about 1400° C., in someembodiments from about 750° C. to about 1200° C., and in someembodiments, from about 800° C. to about 1100° C. Heat treatment mayoccur in an inert or reducing atmosphere. For example, heat treatmentmay occur in an atmosphere containing hydrogen or a hydrogen-releasingcompound (e.g., ammonium chloride, calcium hydride, magnesium hydride,etc.) to partially sinter the powder and decrease the content ofimpurities (e.g., fluorine). If desired, agglomeration may also beperformed in the presence of a getter material, such as magnesium. Afterthermal treatment, the particles may be passivated by the gradualadmission of air. Other suitable agglomeration techniques are alsodescribed in U.S. Pat. No. 6,576,038 to Rao; U.S. Pat. No. 6,238,456 toWolf, et al.; U.S. Pat. No. 5,954,856 to Pathare, et al.; U.S. Pat. No.5,082,491 to Rerat; U.S. Pat. No. 4,555,268 to Getz; U.S. Pat. No.4,483,819 to Albrecht, et al.; U.S. Pat. No. 4,441,927 to Getz, et al.;and U.S. Pat. No. 4,017,302 to Bates, et al.

Certain additional components may also be included in the powder. Forexample, the powder may be optionally mixed with a binder and/orlubricant to ensure that the particles adequately adhere to each otherwhen pressed. Suitable binders may include, for instance, poly(vinylbutyral); poly(vinyl acetate); poly(vinyl alcohol); poly(vinylpyrrolidone); cellulosic polymers, such as carboxymethylcellulose,methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, andmethylhydroxyethyl cellulose; atactic polypropylene, polyethylene;polyethylene glycol (e.g., Carbowax™ from Dow Chemical Co.);polystyrene, poly(butadiene/styrene); polyamides, polyimides, andpolyacrylamides, high molecular weight polyethers; copolymers ofethylene oxide and propylene oxide; fluoropolymers, such aspolytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefincopolymers; acrylic polymers, such as sodium polyacrylate, poly(loweralkyl acrylates), poly(lower alkyl methacrylates) and copolymers oflower alkyl acrylates and methacrylates; and fatty acids and waxes, suchas stearic and other soapy fatty acids, vegetable wax, microwaxes(purified paraffins), etc. The binder may be dissolved and dispersed ina solvent. Exemplary solvents may include water, alcohols, and so forth.When utilized, the percentage of binders and/or lubricants may vary fromabout 0.1% to about 8% by weight of the total mass. It should beunderstood, however, that binders and/or lubricants are not necessarilyrequired in the present invention.

The resulting powder may be compacted using any conventional powderpress mold. For example, the press mold may be a single stationcompaction press using a die and one or multiple punches. Alternatively,anvil-type compaction press molds may be used that use only a die andsingle lower punch. Single station compaction press molds are availablein several basic types, such as cam, toggle/knuckle and eccentric/crankpresses with varying capabilities, such as single action, double action,floating die, movable platen, opposed ram, screw, impact, hot pressing,coining or sizing. The powder may be compacted around an anode lead(e.g., tantalum wire). It should be further appreciated that the anodelead may alternatively be attached (e.g., welded) to the anode bodysubsequent to pressing and/or sintering of the anode body.

If desired, any binder/lubricant may be removed after compression, suchas by heating the formed pellet under vacuum at a certain temperature(e.g., from about 150° C. to about 500° C.) for several minutes.Alternatively, the binder/lubricant may also be removed by contactingthe pellet with an aqueous solution, such as described in U.S. Pat. No.6,197,252 to Bishop, et al., which is incorporated herein in itsentirety by reference thereto for all purposes. Regardless, the pressedanode body is sintered to form a porous, integral mass. The sinteringconditions may be within the ranges noted above.

The sintered anode body may then be anodically oxidized (“anodized”) sothat a dielectric layer is formed over and/or within the anode. Forexample, a tantalum (Ta) anode body may be anodized to form a dielectriclayer of tantalum pentoxide (Ta₂O₅). Anodization may be performed byinitially applying an electrolyte to the anode body, such as by dippingthe anode body into a bath that contains the electrolyte, and thenapplying a current. The electrolyte is generally in the form of aliquid, such as a solution (e.g., aqueous or non-aqueous), dispersion,melt, etc. A solvent is generally employed in the electrolyte, such aswater (e.g., deionized water); ethers (e.g., diethyl ether andtetrahydrofuran); alcohols (e.g., methanol, ethanol, n-propanol,isopropanol, and butanol); triglycerides; ketones (e.g., acetone, methylethyl ketone, and methyl isobutyl ketone); esters (e.g., ethyl acetate,butyl acetate, diethylene glycol ether acetate, and methoxypropylacetate); amides (e.g., dimethylformamide, dimethylacetamide,dimethylcaprylic/capric fatty acid amide and N-alkylpyrrolidones);nitriles (e.g., acetonitrile, propionitrile, butyronitrile andbenzonitrile); sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO)and sulfolane); and so forth. The solvent may constitute from about 50wt. % to about 99.9 wt. %, in some embodiments from about 75 wt. % toabout 99 wt. %, and in some embodiments, from about 80 wt. % to about 95wt. % of the electrolyte. Although not necessarily required, the use ofan aqueous solvent (e.g., water) is often desired to facilitateformation of an oxide. In fact, water may constitute about 1 wt. % ormore, in some embodiments about 10 wt. % or more, in some embodimentsabout 50 wt. % or more, in some embodiments about 70 wt. % or more, andin some embodiments, about 90 wt. % to 100 wt. % of the solvent(s) usedin the electrolyte.

The electrolyte is electrically conductive and may have an electricalconductivity of about 0.05 milliSiemens per centimeter (“mS/cm”) ormore, in some embodiments about 0.1 mS/cm or more, and in someembodiments, from about 0.2 mS/cm to about 100 mS/cm, determined at atemperature of 25° C. To enhance the electrical conductivity of theelectrolyte, a compound may be employed that is capable of dissociatingin the solvent to form ions. Suitable ionic compounds for this purposemay include, for instance, acids, such as hydrochloric acid, nitricacid, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid,boronic acid, etc.; organic acids, including carboxylic acids, such asacrylic acid, methacrylic acid, malonic acid, succinic acid, salicylicacid, sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleicacid, gallic acid, tartaric acid, citric acid, formic acid, acetic acid,glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalicacid, glutaric acid, gluconic acid, lactic acid, aspartic acid,glutaminic acid, itaconic acid, trifluoroacetic acid, barbituric acid,cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid,etc.; sulfonic acids, such as methanesulfonic acid, benzenesulfonicacid, toluenesulfonic acid, trifluoromethanesulfonic acid,styrenesulfonic acid, naphthalene disulfonic acid,hydroxybenzenesulfonic acid, dodecylsulfonic acid,dodecylbenzenesulfonic acid, etc.; polymeric acids, such aspoly(acrylic) or poly(methacrylic) acid and copolymers thereof (e.g.,maleic-acrylic, sulfonic-acrylic, and styrene-acrylic copolymers),carageenic acid, carboxymethyl cellulose, alginic acid, etc.; and soforth. The concentration of ionic compounds is selected to achieve thedesired electrical conductivity. For example, an acid (e.g., phosphoricacid) may constitute from about 0.01 wt. % to about 5 wt. %, in someembodiments from about 0.05 wt. % to about 0.8 wt. %, and in someembodiments, from about 0.1 wt. % to about 0.5 wt. % of the electrolyte.If desired, blends of ionic compounds may also be employed in theelectrolyte.

A current is passed through the electrolyte to form the dielectriclayer. The value of voltage manages the charge (current multiplied bytime) and thereby the thickness of the dielectric layer. For example,the power supply may be initially set up at a galvanostatic mode untilthe required voltage is reached. Thereafter, the power supply may beswitched to a potentiostatic mode in which the voltage is held constantto ensure that the desired dielectric thickness is formed on the anodebody. Of course, other known methods may also be employed, such as pulsemethods. Regardless, to help achieve the desired thickness for thedielectric layer, the forming voltage used during anodization, which istypically equal to the peak voltage, is typically high, such as about150 volts or more, in some embodiments from about 200 volts to about 350volts, and in some embodiments, from about 220 to about 320 volts. Thevoltage level may vary (e.g., increasing) or remain constant within thisrange. The temperature of the anodizing solution may range from about10° C. to about 200° C., in some embodiments from about 20° C. to about150° C., and in some embodiments, from about 30° C. to about 100° C.

The size of the resulting anode may depend in part on the desired sizeof the capacitor. In certain embodiments, the length of the anode bodymay range from about 10 to about 200 millimeters, in some embodimentsfrom about 15 to about 150 millimeters, and in some embodiments, fromabout 20 to about 120 millimeters. The width (or diameter) of the anodemay also range from about 0.5 to about 20 millimeters, in someembodiments from about 1 to about 20 millimeters, and in someembodiments, from about 2 to about 10 millimeters. The length of thecapacitor may likewise range from about 20 to about 300 millimeters, insome embodiments from about 40 to about 200 millimeters, and in someembodiments, from about 50 to about 150 millimeters. The width (ordiameter) of the capacitor may also range from about 1 to about 30millimeters, in some embodiments from about 2 to about 20 millimeters,and in some embodiments, from about 5 to about 15 millimeters.

II. Cathode

The cathode(s) of the capacitor generally contains anelectrochemically-active material, which may be coated onto a metalsubstrate. The metal substrate may form the all or a portion of casingfor the capacitor, or it may simply be a separate material (e.g., foil,sheet, screen, mesh, etc.) that is disposed in proximity to an anode.Regardless, the metal used to form the casing and/or metal substrate mayinclude, for instance, tantalum, niobium, aluminum, nickel, hafnium,titanium, copper, silver, steel (e.g., stainless), alloys thereof,composites thereof (e.g., metal coated with electrically conductiveoxide), and so forth. Tantalum is particularly suitable for use in thepresent invention. If desired, a surface of the substrate may beroughened to increase its surface area and increase the degree to whicha material may be able to adhere thereto. In one embodiment, forexample, a surface of the substrate is chemically etched, such as byapplying a solution of a corrosive substance (e.g., hydrochloric acid)to the surface. Mechanical roughening may also be employed. Forinstance, a surface of the substrate may be abrasive blasted bypropelling a stream of abrasive media (e.g., sand) against at least aportion of a surface thereof.

Once formed, an electrochemically-active material is applied to themetal substrate to increase the effective surface area (e.g.,carbonaceous particles) and/or provide pseudo-capacitance (e.g.,conductive polymers, ruthenium oxide, etc.) to produce a highcapacitance cathode with which the electrolyte electrochemicallycommunicates with the substrate. Such a high capacity cathode materialallows for the formation of capacitors with maximized capacitance for agiven size and/or capacitors with a reduced size for a givencapacitance. The nature of the electrochemically-active material mayvary. For example, a particulate material may be employed that includesconductive particles, such as those formed from tantalum, ruthenium,iridium, nickel, rhodium, rhenium, cobalt, tungsten, manganese,tantalum, niobium, molybdenum, lead, titanium, platinum, palladium, andosmium, as well as combinations of these metals. Non-insulating oxideconductive particles may also be employed. Suitable oxides may include ametal selected from the group consisting of ruthenium, iridium, nickel,rhodium, rhenium, cobalt, tungsten, manganese, tantalum, niobium,molybdenum, lead, titanium, platinum, palladium, and osmium, as well ascombinations of these metals. Particularly suitable metal oxides includeruthenium dioxide, niobium oxide, niobium dioxide, iridium oxide, andmanganese dioxide. Carbonaceous particles may also be employed that havethe desired level of conductivity, such as activated carbon, carbonblack, graphite, etc. Some suitable forms of activated carbon andtechniques for formation thereof are described in U.S. Pat. No.5,726,118 to Ivey, et al. and U.S. Pat. No. 5,858,911 to Wellen, et al.

If desired, the particles may be sintered together and/or to thesubstrate so that they form a more integral and robust coating. Forexample, tantalum particles may be employed that form a “sleeve” overthe metal substrate. Sintering may be conducted at a wide variety oftemperatures, such as from about 800° C. to about 2000° C., in someembodiments from about 1200° C. to about 1800° C., and in someembodiments, from about 1500° C. to about 1700° C., for a time of fromabout 5 minutes to about 100 minutes, and in some embodiments, fromabout 10 minutes to about 50 minutes. This may occur in one or moresteps. If desired, sintering may occur in a reducing atmosphere, such asin a vacuum, inert gas, hydrogen, etc. The reducing atmosphere may be ata pressure of from about 10 Torr to about 2000 Torr, in some embodimentsfrom about 100 Torr to about 1000 Torr, and in some embodiments, fromabout 100 Torr to about 930 Torr. Mixtures of hydrogen and other gases(e.g., argon or nitrogen) may also be employed.

A conductive polymer coating may also be employed as theelectrochemically-active material. The conductive polymer coating may beformed from one or more layers. The material employed in such layer(s)may vary. In one embodiment, for example, the material includesconductive polymer(s) that are typically π-conjugated and haveelectrical conductivity after oxidation or reduction. Examples of suchπ-conjugated conductive polymers include, for instance, polyheterocycles(e.g., polypyrroles, polythiophenes, polyanilines, etc.),polyacetylenes, poly-p-phenylenes, polyphenolates, and so forth.Substituted polythiophenes are particularly suitable for use asconductive polymer in that they have particularly good mechanicalrobustness and electrical performance. In one particular embodiment, thesubstituted polythiophene has the following general structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, optionally substituted C₁ to C₁₈ alkylradical (e.g., methyl, ethyl, n- or iso-propyl, n-, iso-, sec- ortert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl,n-octadecyl, etc.); optionally substituted C₅ to C₁₂ cycloalkyl radical(e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononylcyclodecyl, etc.); optionally substituted C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); optionally substituted C₇ to C₁₈ aralkylradical (e.g., benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-,3,5-xylyl, mesityl, etc.); optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0; and

n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in someembodiments, from 5 to 1,000. Example of substituents for the radicals“D” or “R₇” include, for instance, alkyl, cycloalkyl, aryl, aralkyl,alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone,sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylicacid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilanegroups, carboxylamide groups, and so forth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

Methods for forming conductive polymers, such as described above, arewell known in the art. For instance, U.S. Pat. No. 6,987,663 to Merker,et al. describes various techniques for forming substitutedpolythiophenes from a monomeric precursor. The monomeric precursor may,for instance, have the following structure:

wherein,

T, D, R₇, and q are defined above. Particularly suitable thiophenemonomers are those in which “D” is an optionally substituted C₂ to C₃alkylene radical. For instance, optionally substituted3,4-alkylenedioxythiophenes may be employed that have the generalstructure:

wherein, R₇ and q are as defined above.

In one particular embodiment, “q” is 0. One commercially suitableexample of 3,4-ethylenedioxthiophene is available from Heraeus Cleviosunder the designation Clevios™. In yet another particular embodiment,“q” is 1. For example, an alkyl-substitutedpoly(3,4-dioxyethylenethiophene) may be employed. One example of such apolymer is one in which R₇ in the formula above is (CH₂)_(y)—OR₂,wherein y is from 1 to 10, in some embodiments from 1 to 5, in someembodiments, from 1 to 3, and in some embodiments, from 1 to 2 (e.g.,2); and R₂ is hydrogen or an alkyl group. Particular examples of suchpolymers include hydroxyethylated poly(3,4-ethylenedioxythiophene) (y is2 and R₂ is H) and hydroxymethylated poly(3,4-ethylenedioxthiophene) (yis 1 and R₂ is H).

The thiophene monomers may be chemically polymerized in the presence ofan oxidative catalyst. The oxidative catalyst typically includes atransition metal cation, such as iron(III), copper(II), chromium(VI),cerium(IV), manganese(IV), manganese(VII), ruthenium(III) cations, etc.A dopant may also be employed to provide excess charge to the conductivepolymer and stabilize the conductivity of the polymer. The dopanttypically includes an inorganic or organic anion, such as an ion of asulfonic acid. In certain embodiments, the oxidative catalyst employedin the precursor solution has both a catalytic and doping functionalityin that it includes a cation (e.g., transition metal) and anion (e.g.,sulfonic acid). For example, the oxidative catalyst may be a transitionmetal salt that includes iron(III) cations, such as iron(III) halides(e.g., FeCl₃) or iron(III) salts of other inorganic acids, such asFe(ClO₄)₃ or Fe₂(SO₄)₃ and the iron(III) salts of organic acids andinorganic acids comprising organic radicals. Examples of iron (III)salts of inorganic acids with organic radicals include, for instance,iron(III) salts of sulfuric acid monoesters of C₁ to C₂₀ alkanols (e.g.,iron(III) salt of lauryl sulfate). Likewise, examples of iron(III) saltsof organic acids include, for instance, iron(III) salts of C₁ to C₂₀alkane sulfonic acids (e.g., methane, ethane, propane, butane, ordodecane sulfonic acid); iron (III) salts of aliphatic perfluorosulfonicacids (e.g., trifluoromethane sulfonic acid, perfluorobutane sulfonicacid, or perfluorooctane sulfonic acid); iron (III) salts of aliphaticC₁ to C₂₀ carboxylic acids (e.g., 2-ethylhexylcarboxylic acid); iron(III) salts of aliphatic perfluorocarboxylic acids (e.g.,trifluoroacetic acid or perfluorooctane acid); iron (III) salts ofaromatic sulfonic acids optionally substituted by C₁ to C₂₀ alkyl groups(e.g., benzene sulfonic acid, o-toluene sulfonic acid, p-toluenesulfonic acid, or dodecylbenzene sulfonic acid); iron (III) salts ofcycloalkane sulfonic acids (e.g., camphor sulfonic acid); and so forth.Mixtures of these above-mentioned iron(III) salts may also be used.Iron(III)-p-toluene sulfonate, iron(III)-o-toluene sulfonate, andmixtures thereof, are particularly suitable. One commercially suitableexample of iron(III)-p-toluene sulfonate is available from HeraeusClevios under the designation Clevios™ C.

Various methods may be utilized to form a conductive polymer layer. Inone embodiment, the oxidative catalyst and monomer are applied, eithersequentially or together, such that the polymerization reaction occursin situ on the substrate. Suitable application techniques may includescreen-printing, dipping, electrophoretic coating, and spraying, may beused to form a conductive polymer coating. As an example, the monomermay initially be mixed with the oxidative catalyst to form a precursorsolution. Once the mixture is formed, it may be applied to the substrateand then allowed to polymerize so that the conductive coating is formedon the surface. Alternatively, the oxidative catalyst and monomer may beapplied sequentially. In one embodiment, for example, the oxidativecatalyst is dissolved in an organic solvent (e.g., butanol) and thenapplied as a dipping solution. The substrate may then be dried to removethe solvent therefrom. Thereafter, the substrate may be dipped into asolution containing the monomer. Polymerization is typically performedat temperatures of from about −10° C. to about 250° C., and in someembodiments, from about 0° C. to about 200° C., depending on theoxidizing agent used and desired reaction time. Suitable polymerizationtechniques, such as described above, may be described in more detail inU.S. Pat. No. 7,515,396 to Biler. Still other methods for applying suchconductive coating(s) may be described in U.S. Pat. No. 5,457,862 toSakata, et al., U.S. Pat. No. 5,473,503 to Sakata, et al., U.S. Pat. No.5,729,428 to Sakata, et al., and U.S. Pat. No. 5,812,367 to Kudoh, etal.

The total target thickness of the electrochemically-active coating maygenerally vary depending on the desired properties of the capacitor.Typically, the coating has a thickness of from about 0.2 micrometers(“μm”) to about 50 μm, in some embodiments from about 0.5 μm to about 20μm, and in some embodiments, from about 1 μm to about 5 μm. Regardless,the resulting cathode, including the substrate andelectrochemically-active material may have a relatively small thickness.For example, the cathode may have a thickness ranging from about 10micrometers to about 2000 micrometers, in some embodiments from about 20micrometers to about 1500 micrometers, and in some embodiments, fromabout 30 micrometers to about 1000 micrometers.

III. Working Electrolyte

The working electrolyte may be impregnated within the anode, or it maybe added to the capacitor at a later stage of production. Theelectrolyte generally uniformly wets the dielectric on the anode.Various suitable electrolytes are described in U.S. Pat. Nos. 5,369,547and 6,594,140 to Evans, et al. Typically, the electrolyte is ionicallyconductive in that has an electrical conductivity of from about 0.005 toabout 1 Siemens per centimeter (“S/cm”), in some embodiments from about0.01 to about 0.1 S/cm, and in some embodiments, from about 0.02 toabout 0.05 S/cm, determined at a temperature of about 23° C. using anyknown electric conductivity meter (e.g., Oakton Con Series 11). Theelectrolyte is generally in the form of a fluid, such as a liquid, suchas a solution (e.g., aqueous or non-aqueous), colloidal suspension, gel,etc. For example, the electrolyte may be an aqueous solution of an acid(e.g., sulfuric acid, phosphoric acid, or nitric acid), base (e.g.,potassium hydroxide), or salt (e.g., ammonium salt, such as a nitrate),as well any other suitable electrolyte known in the art, such as a saltdissolved in an organic solvent (e.g., ammonium salt dissolved in aglycol-based solution). Various other electrolytes are described in U.S.Pat. Nos. 5,369,547 and 6,594,140 to Evans, et al.

The desired ionic conductivity may be achieved by selecting ioniccompound(s) (e.g., acids, bases, salts, and so forth) within certainconcentration ranges. In one particular embodiment, salts of weakorganic acids may be effective in achieving the desired conductivity ofthe electrolyte. The cation of the salt may include monatomic cations,such as alkali metals (e.g., Li⁺, Na⁺, K⁺, Rb⁺, or Cs⁺), alkaline earthmetals (e.g., Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺or Ba²⁺), transition metals (e.g.,Ag⁺, Fe²⁺, Fe³⁺, etc.), as well as polyatomic cations, such as NH₄ ⁺.The monovalent ammonium (NH₄ ⁺), sodium (K⁺), and lithium (Li⁺) areparticularly suitable cations for use in the present invention. Theorganic acid used to form the anion of the salt may be “weak” in thesense that it typically has a first acid dissociation constant (pK_(a1))of about 0 to about 11, in some embodiments about 1 to about 10, and insome embodiments, from about 2 to about 10, determined at about 23° C.Any suitable weak organic acids may be used in the present invention,such as carboxylic acids, such as acrylic acid, methacrylic acid,malonic acid, succinic acid, salicylic acid, sulfosalicylic acid, adipicacid, maleic acid, malic acid, oleic acid, gallic acid, tartaric acid(e.g., dextotartaric acid, mesotartaric acid, etc.), citric acid, formicacid, acetic acid, glycolic acid, oxalic acid, propionic acid, phthalicacid, isophthalic acid, glutaric acid, gluconic acid, lactic acid,aspartic acid, glutaminic acid, itaconic acid, trifluoroacetic acid,barbituric acid, cinnamic acid, benzoic acid, 4-hydroxybenzoic acid,aminobenzoic acid, etc.; blends thereof, and so forth. Polyprotic acids(e.g., diprotic, triprotic, etc.) are particularly desirable for use informing the salt, such as adipic acid (pK_(a1) of 4.43 and pK_(a2) of5.41), α-tartaric acid (pK_(a1) of 2.98 and pK_(a2) of 4.34),meso-tartaric acid (pK_(a1) of 3.22 and pK_(a2) of 4.82), oxalic acid(pK_(a1) of 1.23 and pK_(a2) of 4.19), lactic acid (pK_(a1) of 3.13,pK_(a2) of 4.76, and pK_(a3) of 6.40), etc.

While the actual amounts may vary depending on the particular saltemployed, its solubility in the solvent(s) used in the electrolyte, andthe presence of other components, such weak organic acid salts aretypically present in the electrolyte in an amount of from about 0.1 toabout 25 wt. %, in some embodiments from about 0.2 to about 20 wt. %, insome embodiments from about 0.3 to about 15 wt. %, and in someembodiments, from about 0.5 to about 5 wt. %.

The electrolyte is typically aqueous in that it contains an aqueoussolvent, such as water (e.g., deionized water). For example, water(e.g., deionized water) may constitute from about 20 wt. % to about 95wt. %, in some embodiments from about 30 wt. % to about 90 wt. %, and insome embodiments, from about 40 wt. % to about 85 wt. % of theelectrolyte. A secondary solvent may also be employed to form a solventmixture. Suitable secondary solvents may include, for instance, glycols(e.g., ethylene glycol, propylene glycol, butylene glycol, triethyleneglycol, hexylene glycol, polyethylene glycols, ethoxydiglycol,dipropyleneglycol, etc.); glycol ethers (e.g., methyl glycol ether,ethyl glycol ether, isopropyl glycol ether, etc.); alcohols (e.g.,methanol, ethanol, n-propanol, iso-propanol, and butanol); ketones(e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters(e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate,methoxypropyl acetate, ethylene carbonate, propylene carbonate, etc.);amides (e.g., dimethylformamide, dimethylacetamide,dimethylcaprylic/capric fatty acid amide and N-alkylpyrrolidones);sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO) and sulfolane);and so forth. Such solvent mixtures typically contain water in an amountfrom about 40 wt. % to about 80 wt. %, in some embodiments from about 50wt. % to about 75 wt. %, and in some embodiments, from about 55 wt. % toabout 70 wt. % and secondary solvent(s) in an amount from about 20 wt. %to about 60 wt. %, in some embodiments from about 25 wt. % to about 50wt. %, and in some embodiments, from about 30 wt. % to about 45 wt. %.The secondary solvent(s) may, for example, constitute from about 5 wt. %to about 45 wt. %, in some embodiments from about 10 wt. % to about 40wt. %, and in some embodiments, from about 15 wt. % to about 35 wt. % ofthe electrolyte.

If desired, the electrolyte may be relatively neutral and have a pH offrom about 4.5 to about 8.0, in some embodiments from about 5.0 to about7.5, and in some embodiments, from about 5.5 to about 7.0. One or morepH adjusters (e.g., acids, bases, etc.) may be employed to help achievethe desired pH. In one embodiment, an acid is employed to lower the pHto the desired range. Suitable acids include, for instance, organicacids such as described above; inorganic acids, such as hydrochloricacid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid,boric acid, boronic acid, etc.; and mixtures thereof. Although the totalconcentration of pH adjusters may vary, they are typically present in anamount of from about 0.01 wt. % to about 10 wt. %, in some embodimentsfrom about 0.05 wt. % to about 5 wt. %, and in some embodiments, fromabout 0.1 wt. % to about 2 wt. % of the electrolyte.

The electrolyte may also contain other components that help improve theelectrical performance of the capacitor. For instance, a depolarizer maybe employed in the electrolyte to help inhibit the evolution of hydrogengas at the cathode of the electrolytic capacitor, which could otherwisecause the capacitor to bulge and eventually fail. When employed, thedepolarizer normally constitutes from about 1 to about 500 parts permillion (“ppm”), in some embodiments from about 10 to about 200 ppm, andin some embodiments, from about 20 to about 150 ppm of the electrolyte.Suitable depolarizers may include nitroaromatic compounds, such as2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzonic acid,3-nitrobenzonic acid, 4-nitrobenzonic acid, 2-nitroace tophenone,3-nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole,3-nitroanisole, 4-nitroanisole, 2-nitrobenzaldehyde,3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol,3-nitrobenzyl alcohol, 4-nitrobenzyl alcohol, 2-nitrophthalic acid,3-nitrophthalic acid, 4-nitrophthalic acid, and so forth. Particularlysuitable nitroaromatic depolarizers for use in the present invention arenitrobenzoic acids, anhydrides or salts thereof, substituted with one ormore alkyl groups (e.g., methyl, ethyl, propyl, butyl, etc.). Specificexamples of such alkyl-substituted nitrobenzoic compounds include, forinstance, 2-methyl-3-nitrobenzoic acid; 2-methyl-6-nitrobenzoic acid;3-methyl-2-nitrobenzoic acid; 3-methyl-4-nitrobenzoic acid;3-methyl-6-nitrobenzoic acid; 4-methyl-3-nitrobenzoic acid; anhydridesor salts thereof; and so forth.

IV. Capacitor Construction

As indicated above, the wet electrolytic capacitor of the presentinvention contains a casing within which the working electrolyte, atleast one cathode, and at least anode are positioned. As indicatedabove, a lid assembly seals the opening of the casing. The lid assemblycontains a lid (e.g., tantalum) that defines an internal orifice. Thelid is typically formed from a metal, such as tantalum, niobium,aluminum, nickel, hafnium, titanium, copper, silver, steel (e.g.,stainless), alloys thereof (e.g., electrically conductive oxides),composites thereof (e.g., metal coated with electrically conductiveoxide), and so forth.

A tube extends through the orifice that is hollow and of a size andshape sufficient to accommodate an anode lead that extends from ananode. The tube is generally formed from a valve metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, silver, alloysthereof (e.g., electrically conductive oxides), and so forth. Notably, adielectric layer is formed on a surface (inner and/or exterior surfaces)of the tube. The dielectric layer may be formed by subjecting the tubeto a voltage to initiate anodic formation (“anodization”) of an oxidefilm (dielectric layer). For example, a tantalum (Ta) tube may beanodized to form a dielectric layer of tantalum pentoxide (Ta₂O₅).Anodization may be performed by initially applying an electrolyte to thetube, such as by dipping the tube into a bath that contains theelectrolyte, and then applying a current. The electrolyte is generallyin the form of a fluid, such as described above. To help achieve thedesired thickness for the dielectric layer as noted above, the formingvoltage is typically, such as about 5 volts or more, in some embodimentsfrom about 5 volts to about 200 volts, 200 volts to about 400 volts, andin some embodiments, from about 250 to about 350 volts. The voltagelevel may vary (e.g., increasing) or remain constant within this range.

Referring to FIG. 1, for example, one embodiment of a lid assembly 2that may be employed in the present invention is shown in more detail.As shown, the lid assembly 2 contains a lid 40 having an upper planarsurface spaced from a lower planar surface. The lid 40 defines aninternal orifice (not shown), which may be cylindrical and of agenerally constant inside diameter. In the illustrated embodiment, theorifice is defined by a cylindrical sidewall spaced inwardly from aninner diameter portion 108 of the lid 40. The sidewall may alternativelybe formed integral with the from a separate ferrule portion connected tothe lid 40. An insulative material (e.g., glass) may be provided withinthe orifice to form a hermetic seal 60 (e.g., glass-to-metal seal)between a tube 80 and the sidewall of the orifice. Although notexpressly shown, a dielectric layer may be formed on an inner surface201 and/or a lower surface 203 of the tube 80 as indicated above.

The particular manner in which the anode(s), cathode(s), and workingelectrolyte are provided within the casing may vary as desired. Anynumber of anodes and cathodes may generally be employed. In oneembodiment, for instance, a single anode may be employed. In such anembodiment, the electrochemically-active material of the cathode may bedisposed on the inner surface of the casing or on a separate metalsubstrate (e.g., foil, sheet, screen, mesh, etc.) that is disposed inproximity to the inner surface of the casing. In other embodiments,however, the capacitor may contain multiple anodes, such as 2 or more,in some embodiments 3 or more, and in some embodiments, from 3 to 6anodes. In one particular embodiment, multiple anodes are employed. Forexample, at least one central anode may be positioned within theinterior of the casing and between first and second outer anodes. Incertain embodiments, the central anode may define first and secondopposing planar sidewalls, and the first and second outer anodes eachdefine a radiused sidewall having a degree of curvature that, in certainembodiments, can correspond to the degree of curvature of thecylindrical sidewall of the casing. The first and second outer anodesalso each define a planar sidewall that opposes the respective radiusedsidewalls and faces a planar sidewall of the central anode. That is, oneplanar sidewall of the central anode faces the planar sidewall of thefirst outer anode and the opposing planar sidewall of the central anodefaces the planar sidewall of the second outer anode. Without intendingto be limited by theory, it is believed that such a geometricconfiguration for the anode can help improve the electrical propertiesof the resulting capacitor, and also to aid in its manufacture. Itshould be understood, however, that others shapes may be employed forthe outer sidewalls. In certain embodiments, for example, the outersidewalls may have rounded corners. Likewise, the outer sidewalls may beradiused. In such embodiments, the planar inner sidewalls may extend ina direction that is generally perpendicular to a line that is tangent tothe radiused outer sidewalls. The number of central anodes may vary asis known in the art. For instance, the capacitor may contain 1 or morecentral anodes, in some embodiments from 1 to 4 central anodes, and insome embodiments, from 1 to 3 central anodes. When multiple centralanodes are employed, they may have the same or different shape. Forexample, one central anode may possess planar sidewalls, while anothermay contain only radiused sidewalls.

Referring to FIGS. 2-4, for example, one example of a capacitor 10containing a central anode 16 positioned between first and second outeranodes 20 a and 20 b is shown in more detail. As depicted, the capacitor10 contains a casing 30 that has a sidewall 33 that extends from abottom end 35 to an upper end 39. In the illustrated embodiment, thesidewall 33 is shown as having a cylindrical shape, but it should beunderstood that other shapes may also be used. Regardless, the casing 30defines an interior within which the central anode 16 and first andsecond outer anodes 20 a and 20 b, respectively, are positioned. Thecentral anode 16 has first and second outer sidewalls 11 and 13 thatintersect first and second planar inner sidewalls 12 and 14 (FIG. 4).Likewise, as shown in FIG. 4, the first outer anode 20 a has a radiusedsidewall 17 a and an opposing planar sidewall 19 a, while the secondouter anode 20 b has a radiused sidewall 17 b and an opposing planarsidewall 19 b. In the illustrated embodiment, the planar sidewall 12 ofthe central anode 16 faces the planar sidewall 17 a of the first outeranode 20 a and the planar sidewall 14 of the central anode 16 faces theplanar sidewall 17 b of the second outer anode 20 b.

The manner in which the anodes are connected can vary. In certainembodiments, for example, anode leads may extend in a longitudinaldirection from each respective anode, which are then connected togetherby welding or other suitable techniques. In one embodiment, forinstance, the anode leads may be connected to a common metal bridge(e.g., bar, hoop, etc.). In yet other embodiments, the leads may bedirectly connected together. In the illustrated embodiment, for example,an anode lead 24 extends from the central anode 16, an anode lead 22extends from the first outer anode 20 a, and an anode lead 26 extendsfrom the second outer anode 20 b. The anode lead 22 has a length that isgreater than the other leads 24 and 26. In this manner, the anode lead22 can be folded over so that it contacts both the anode lead 24 and theanode lead 26. Connection can thus be made at the point of contact. Itshould of course be understood that the other leads may also be foldedin one or more directions to provide the desired point of contact.

As indicated above, at least one cathode is also positioned within thecasing. Referring again to FIGS. 2-4, for instance, a first cathode 32can be disposed in proximity to the inner surface of the casing sidewall33 so that it extends around the perimeter thereof. Additional cathodesmay also be disposed between the anodes. For example, a second cathode31 a may be disposed between the first outer anode 20 a and the centralanode 16, while a third cathode 31 b may be disposed between the secondouter anode 20 b and the central anode 16. Although not shown, thecathodes 32, 31 a, and 31 b may be formed from anelectrochemically-active material that is disposed on a metal substrate(e.g., foil).

If desired, a separator may also be positioned adjacent to the anodes toprevent direct contact between the anode and cathode, yet permit ioniccurrent flow of the electrolyte to the electrodes. Examples of suitablematerials for this purpose include, for instance, porous polymermaterials (e.g., polypropylene, polyethylene, polycarbonate, etc.),porous inorganic materials (e.g., fiberglass mats, porous glass paper,etc.), ion exchange resin materials, etc. Particular examples includeionic perfluoronated sulfonic acid polymer membranes (e.g., Nafion™ fromthe E.I. DuPont de Nemeours & Co.), sulphonated fluorocarbon polymermembranes, polybenzimidazole (PBI) membranes, and polyether ether ketone(PEEK) membranes. Although preventing direct contact between the anodeand cathode, the separator permits ionic current flow of the electrolyteto the electrodes. The location and configuration of a separator mayvary as desired. In the embodiment illustrated in FIGS. 2-4, forinstance, a first separator 38 may be wrapped around the first cathode32 to prevent direct contact with the outer anodes 20 a and 20 b.Likewise, a second separator 37 a may be wrapped around the secondcathode 31 a to prevent direct contact with the first outer anode 20 aand the central anode 16, while a third separator 37 b may be wrappedaround the third cathode 31 b to prevent direct contact with the secondouter anode 20 b and the central anode 16.

Referring again to FIGS. 1-4, for example, the lid assembly 2 may beused to seal the capacitor 10. As shown, the lid assembly 2 contains alid 40 having an upper planar surface spaced from a lower planarsurface. The lower planar surface of the lid 40 is positioned on andoptionally welded to the upper end 39 of the casing sidewall 33 so thatan outer diameter 106 of the lid 40 is coplanar to the outer diameter ofthe casing sidewall 33. If desired, a portion 100 of the cathode 32,cathode 31 a, and/or 31 b may also be positioned between the lid 40 andthe upper end 39 of the casing sidewall 33. The outer diameter 106 ofthe lid 40 also forms a step that leads to an inner diameter portion108. As noted above, the lid assembly 2 also contains the tube 80, whichcan accommodate an anode lead 24 that extends from the central anode 16.

The lid assembly may also optionally include a liquid seal 70 that isformed from a generally insulative sealant material. For example, thesealant material typically has an electrical resistance of about 1×10²ohms-m or more, in some embodiments about 1×10⁵ ohms-m or more, and insome embodiments, from about 1×10¹⁵ to about 1×10²⁵ ohms-m, determinedat a temperature of 20° C. The liquid seal 70 may cover a portion of asurface of the tube 80, and preferably, the entire surface. Examples ofsuitable sealant materials for use in the liquid seal 70 may include,for instance, silicone polymers, flouropolymers, etc. In addition to theliquid seal discussed above, the capacitor of the present invention mayalso contain one or more secondary liquid seals. Referring to FIG. 2,for example, a gasket 90 is shown that is located adjacent to an uppersurface of the central anode 16 and the outer anodes 20 a and 20 b. Thegasket 90 generally has a cylindrical shape and contains a borecoaxially located therein through which the anode lead 24 can extend.The gasket 90 may be formed from any of a variety of insulativematerials, such as described above (e.g., PTFE). An elastomeric washer84 may also be employed as an additional liquid seal. If desired, thewasher 84 may be positioned between the liquid seal 70 and the gasket 90and thereby and help inhibit leakage of the electrolyte therethrough.The elastomeric washer 84 may be formed from an elastomer that isresistant to corrosion by the electrolyte and has sufficient dielectricstrength to withstand the maximum voltage generated by the capacitor.Examples of elastomers that may be employed include butyl rubber,chlorobutyl rubber, ethylene propylene rubber (EPR), ethylene propylenediene rubber (EPDM), fluoroelastomers (e.g., VITON™),polytetrafluoroethylene, polychloroprene rubber, butadiene rubber,nitrile rubber, isoprene rubber, silicone rubber and styrene butadienerubber.

To attach the lid assembly, it is generally positioned such that theliquid seal 70 is adjacent to the elastomeric washer 90. Once in thedesired position, pressure may be applied to the assembly 50 to compressthe elastomeric washer 90 and create a secondary liquid seal.Thereafter, the lid 40 is welded to the sidewall 33 of the casing 30.The anode lead 24 extends through the tube 80 and is sealed thereto atthe outer end by a weld joint (not shown). An external positive lead 50,preferably of nickel, may likewise be welded to the tube 80. Similarly,an external negative lead 98 may be welded to the casing 30.

Regardless of the particular configuration, the resulting capacitor ofthe present invention may exhibit excellent electrical properties. Forexample, the capacitor may exhibit a high volumetric efficiency, such asfrom about 20,000 μF*V/cm³ to about 100,000 μF*V/cm³, in someembodiments from about 30,000 μF*V/cm³ to about 200,000 μF*V/cm³, and insome embodiments, from about 40,000 μF*V/cm³ to about 150,000 μF*V/cm³,determined at a frequency of 120 Hz and at room temperature (e.g., 25°C.). Volumetric efficiency is determined by multiplying the formationvoltage of a part by its capacitance, and then dividing by the productby the volume of the part. For example, a formation voltage may be 175volts for a part having a capacitance of 520 μF, which results in aproduct of 91,000 μF*V. If the part occupies a volume of about 0.8 cm³,this results in a volumetric efficiency of about 113,750 μF*V/cm³.

The capacitor may also exhibit a high energy density that enables itsuitable for use in high pulse applications. Energy density is generallydetermined according to the equation E=½*CV², where C is the capacitancein farads (F) and V is the working voltage of capacitor in volts (V).The capacitance may, for instance, be measured using a capacitance meter(e.g., Keithley 3330 Precision LCZ meter with Kelvin Leads, 2 volts biasand 1 volt signal) at operating frequencies of from 10 to 120 Hz (e.g.,120 Hz) and a temperature of 25° C. For example, the capacitor mayexhibit an energy density of about 2.0 joules per cubic centimeter(J/cm³) or more, in some embodiments about 3.0 J/cm³, in someembodiments from about 3.5 J/cm³ to about 10.0 J/cm³, and in someembodiments, from about 4.0 to about 8.0 J/cm³. The capacitor may alsoexhibit a relatively high “breakdown voltage” (voltage at which thecapacitor fails), such as about 180 volts or more, in some embodimentsabout 200 volts or more, in some embodiments about 250 volts or more,and in some embodiments about 300 volts or more. In addition, theleakage current, which generally refers to the current flowing from oneconductor to an adjacent conductor through an insulator, can bemaintained at relatively low levels. For example, the numerical value ofthe normalized leakage current of a capacitor of the present inventionis, in some embodiments, less than about 2 nA/μF*V, in some embodimentsless than about 1 nA/μ*V, and in some embodiments, less than about 0.5nA/μF*V, where nA is nanoamps and μF*V is the product of the capacitanceand the rated voltage. Leakage current may be measured using a leakagetest meter (e.g., MC 190 Leakage test, Mantracourt Electronics LTD, UK)at a temperature of 25° C. and at a certain rated voltage after acharging time of from about 60 to about 300 seconds. Such normalizedleakage current values may even be maintained for a substantial amountof time at high temperatures, such as described above.

Through a unique and controlled combination of features relating to thecapacitor configuration and sealing assembly, the present inventor hasdiscovered that good electrical properties (e.g., ESR stability) can bemaintained during the capacitor life operation (e.g., 18 years or moreat about 37° C.). For instance, the capacitor of the present inventionmay exhibit an ESR of about 3,000 milliohms or less, in some embodimentsless than about 2,000 milliohms, in some embodiments from about 1 toabout 1,000 milliohms, and in some embodiments, from about 50 to about800 milliohms, measured with a 2-volt bias and 1-volt signal at afrequency of 120 Hz.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A wet electrolytic capacitor comprising: a casingthat contains a sidewall extending to an upper end to define an opening,wherein the sidewall further defines an inner surface that surrounds aninterior; at least one anode and at least one cathode positioned withinthe interior of the casing, wherein the cathode contains anelectrochemically-active material and further wherein an anode leadextends from the anode; a working electrolyte that is in electricalcontact with the anode and the electrochemically-active material; a lidassembly that contains a lid positioned on an upper end of the casingsidewall, wherein the lid defines an orifice through which a tubeextends, wherein the tube accommodates the anode lead that extends fromthe anode, and further wherein a dielectric layer is formed on a surfaceof the tube.
 2. The wet electrolytic capacitor of claim 1, wherein thedielectric layer is formed on an inner surface of the tube, a lowersurface of the tube, or both.
 3. The wet electrolytic capacitor of claim1, wherein the dielectric layer has a thickness of from about 30 toabout 500 nanometers.
 4. The wet electrolytic capacitor of claim 1,wherein the anode contains a sintered porous body on which a dielectriclayer is formed.
 5. The wet electrolytic capacitor of claim 1, whereinthe tube is formed from a valve metal.
 6. The wet electrolytic capacitorof claim 5, wherein the valve metal is tantalum.
 7. The wet electrolyticcapacitor of claim 1, wherein the anode includes tantalum.
 8. The wetelectrolytic capacitor of claim 1, wherein the sidewall has acylindrical shape.
 9. The wet electrolytic capacitor of claim 1, whereinthe electrochemically-active material includes a conductive polymer. 10.The wet electrolytic capacitor of claim 1, wherein theelectrochemically-active material includes sintered tantalum particles.11. The wet electrolytic capacitor of claim 1, wherein theelectrochemically-active material is coated onto a metal substrate. 12.The wet electrolytic capacitor of claim 11, wherein the metal substrateis formed from tantalum.
 13. The wet electrolytic capacitor of claim 1,wherein the cathode is disposed in proximity to an inner surface of thecasing sidewall.
 14. The wet electrolytic capacitor of claim 1, whereinthe electrolyte is aqueous and has a pH of from about 4.5 to about 8.0.15. The wet electrolytic capacitor of claim 1, wherein the capacitorcontains multiple anodes positioned within the interior of the casing.16. The wet electrolytic capacitor of claim 15, wherein the capacitorcontains first and second outer anodes positioned within the interior ofthe casing and a central anode positioned within the interior of thecasing between the first and second outer anodes.
 17. The wetelectrolytic capacitor of claim 16, wherein an anode lead extends fromthe central anode, the first outer anode, and the second outer anode,respectively.
 18. The wet electrolytic capacitor of claim 17, whereinthe anode lead extending from the first outer anode is folded to contactthe anode lead extending from the central anode and the anode leadextending from the second outer anode.
 19. The wet electrolyticcapacitor of claim 16, wherein a first cathode is disposed in proximityto an inner surface of the casing sidewall.
 20. The wet electrolyticcapacitor of claim 19, wherein a second cathode is disposed between thefirst outer anode and the central anode and a third cathode is disposedbetween the second outer anode and the central anode.
 21. The wetelectrolytic capacitor of claim 1, further comprising an externalpositive lead that is sealed at an end of the tube and an externalnegative lead that is sealed to the casing.
 22. The wet electrolyticcapacitor of claim 1, wherein an insulative material is provided withinthe orifice to form a hermetic seal between the tube and a sidewall ofthe orifice.
 23. The wet electrolytic capacitor of claim 1, furthercomprising a liquid seal that covers at least a portion of the tube. 24.The wet electrolytic capacitor of claim 1, further comprising a gasketthat is positioned adjacent to an upper surface of the anode.
 25. Thewet electrolytic capacitor of claim 24, further comprising anelastomeric washer that is positioned adjacent to the gasket.